ADHD medication side effects in the first 3 months: what to expect week by week

Side effects in the first three months on ADHD medication follow a rough pattern: a strong first impression, a rockier settling phase around weeks 2 to 4, then a steadier picture by month 3. Most side effects are manageable and expected. This guide walks through what tends to happen week by week, including the Vyvanse “honeymoon period”, and when to contact your GP.

In this article

• What to expect, week by week
• The first day and first week on Vyvanse
• Why the honeymoon phase fades
• Weeks 2 to 4: the settling phase
• Common side effects and how to manage them
• Dose adjustments: how your GP fine-tunes treatment
• GP conversations that help vs the ones that do not
• What stable looks like after 3 months
• Frequently asked questions

What to expect, week by week

If you’ve read about Adderall online, know that Australian GPs prescribe dexamphetamine, Vyvanse or methylphenidate instead. See our guide to where GPs can prescribe ADHD medication, state by state, for what’s actually available here.

The first day and first week on Vyvanse

The first day on medication, Priya listened to an entire podcast without rewinding. She read a chapter of a book. She finished her tax return in one sitting. After decades of a brain that wouldn’t cooperate, something had shifted.

This is a composite scenario based on common patient experiences. It does not represent any individual patient.

Priya’s GP started her on 20 mg lisdexamfetamine (Vyvanse), lower than the product information’s standard 30 mg starting dose. Starting lower is a legitimate clinical choice some GPs make, particularly for a first stimulant trial, and Priya’s GP planned to review and adjust from there. Response varies by person and by dose, but in one large randomised trial of adults, measurable improvement in ADHD symptoms was already established within the first week of treatment (Adler et al. 2008, Journal of Clinical Psychiatry 69(9):1364-1373, PMID 19012818). Clinicians sometimes call an early, dramatic-feeling response the “honeymoon phase”, because the contrast with baseline feels so large.

Timing matters for how the first week feels. Taking Vyvanse too late in the day can push sleep onset back. Our guide to getting the best results from Vyvanse covers dosing time and what to do if the timing isn’t working for you.

Why the honeymoon phase fades

The honeymoon fades, and this is normal. Over the following days and weeks, your brain adjusts to the new dopamine baseline. The medication is still working, but the dramatic contrast disappears. What remains is a more subtle improvement in function that people sometimes mistake for the medication “stopping working”. It hasn’t. The novelty has worn off, but the therapeutic effect continues.

Patients report being able to follow conversations, finish tasks they’ve been avoiding for months, and sit through a film without checking their phone during the early days. Some describe a feeling of calm they haven’t experienced before. Once the honeymoon passes, the day-to-day improvement is usually still there, just less dramatic.

Weeks 2 to 4: the settling phase

For Priya, weeks 2 to 4 were the hardest. The cognitive benefits were still present but less pronounced. The side effects were at their peak. She felt caught between “this is helping” and “I do not feel right.”

During this phase, the body is recalibrating. Appetite, sleep, cardiovascular response and mood regulation all adjust to the presence of a stimulant. The Australian ADHD guideline says your GP should review your progress regularly during this period, without setting a fixed interval, because side effects are most prominent, and most manageable, with timely intervention.

Priya’s settling phase included:

• Days 7 to 14: appetite suppression peaked. She skipped lunch most days without realising it, then felt lightheaded by 3pm.
• Days 10 to 21: sleep onset delay. The medication’s effect lasted longer than expected, and she couldn’t fall asleep before midnight.
• Days 14 to 28: a mild afternoon “crash” as the medication wore off. Irritability and fatigue appeared around 4 to 5pm daily.
• Throughout: a resting heart rate a little higher than her baseline (stimulants raise heart rate by an average of about 3 to 6 beats per minute), which her GP monitored at each review.

Appetite change and some sleep disruption are both common during this phase. Both typically improve over the following weeks as the body adapts.

Common side effects and how to manage them

Most stimulant side effects are dose-dependent and manageable. The key is having a GP who knows what to expect, communicates the timeline, and adjusts proactively rather than reactively.

Appetite suppression. The most common side effect. Stimulants suppress hunger signals, particularly while the medication is at peak concentration. Practical strategies: eat a solid breakfast before the medication takes effect, set a lunch alarm, and eat a larger dinner. Priya’s GP suggested high-calorie, low-volume snacks (nuts, cheese, smoothies) for days when eating a full meal felt impossible.

Sleep disruption. Stimulants taken too late in the day interfere with sleep onset. For lisdexamfetamine (Vyvanse), the general rule is to take it early in the morning so the active metabolite clears by bedtime. Priya’s GP moved her dosing time earlier, which resolved most of her sleep issues within a week.

Elevated heart rate and blood pressure. Stimulant medicines cause a modest average increase in blood pressure (about 2 to 4 mmHg) and heart rate (about 3 to 6 beats per minute); some people have larger increases. The average change alone isn’t expected to cause short-term problems, but your GP monitors for bigger changes at each review. The Australian ADHD guideline says heart rate and blood pressure should be checked before and after every dose change, and at least every 6 months. See our guide to how GPs monitor ADHD medication for the full schedule.

Afternoon crash. As the medication wears off, some adults experience a rebound effect: a temporary worsening of ADHD symptoms, irritability, or fatigue. Strategies include dose timing adjustments, switching to a different release profile, or a small afternoon booster dose. Priya’s crash resolved when her GP increased her dose, which extended the medication’s effective window.

Emotional blunting. Some adults report feeling “flat” or “robotic” on stimulants, losing the emotional range they’re used to. This is a sign the dose is too high or the medication isn’t the right fit. Priya didn’t experience this, but her GP had flagged it as something to watch for. If it occurs, the GP reduces the dose or trials a different stimulant class.

Dose adjustments: how your GP fine-tunes treatment

ADHD medication rarely works perfectly at the first dose. The general approach is to start low, increase gradually, and stop when symptoms improve and side effects are tolerable.

Priya’s titration timeline:

1. Weeks 1 to 2: 20 mg lisdexamfetamine. Noticeable benefit for focus and task initiation. Significant appetite suppression and sleep disruption.
2. Week 2 review: GP moved dosing earlier in the morning. Added a breakfast-before-medication rule. Scheduled the next review for week 4.
3. Weeks 3 to 4: Sleep improved. Appetite still reduced but manageable with scheduled eating. Afternoon crash emerging by mid-afternoon.
4. Week 4 review: GP increased the dose to 30 mg based on symptom reports and tolerability. Reviewed blood pressure and heart rate, both within normal range.
5. Weeks 5 to 8: 30 mg provided longer symptom coverage into the late afternoon. Appetite stabilised. Sleep pattern normalised. No emotional blunting.
6. Week 8 review: GP confirmed a stable response. Moved to a longer, individualised review schedule. Discussed the long-term monitoring plan.
7. Month 3: Stable. Consistent benefit without significant side effects.

If the first medication doesn’t work, or produces intolerable side effects, the GP trials the other stimulant class. Between the two, most adults find an effective option. For the small number who don’t respond to either stimulant class, non-stimulant options like atomoxetine or guanfacine are available. See our guide to how GPs choose between dexamphetamine, Vyvanse and Ritalin.

GP conversations that help vs the ones that do not

Priya’s experience was shaped by having a GP who understood ADHD medication management. Not all medication journeys go this smoothly. The difference often comes down to the quality of the clinical conversation.

Conversations that help:

• “These side effects are expected in the first 2 weeks and usually settle. Here is what to do in the meantime.” (Sets expectations and provides strategies.)
• “Describe what the medication does between waking and bedtime, hour by hour.” (Helps the GP understand the medication’s effective window and when to adjust.)
• “How is your appetite? When did you last eat a full meal?” (Proactive screening for the most common side effect.)
• “The honeymoon phase has passed, but the medication is still working. The improvement you see now is the real baseline.” (Prevents premature dose escalation.)

Conversations that do not help: “If you are having side effects, we should stop the medication.” Side effects in the first 2 weeks are expected, not necessarily a reason to abandon treatment unless they are severe.

The GP prescribing pathways now open in several states exist because ADHD medication management requires clinical expertise and an ongoing relationship. A GP who understands titration, side effect timelines, and the difference between a honeymoon ending and medication failure is the difference between a successful treatment journey and an abandoned one.

What stable looks like after 3 months

“Stable” doesn’t mean perfect. At the 3-month mark, Priya described her experience like this: “The medication doesn’t make me a different person. I still lose my keys sometimes. I still get distracted. But I can catch myself and come back to what I was doing.”

Stable ADHD medication after 3 months typically looks like:

• Consistent improvement in task initiation, sustained attention and working memory
• Side effects either resolved or manageable (mild appetite suppression is common long term but not disruptive)
• Emotional regulation improved but not flattened
• Sleep pattern normalised, with appropriate dosing time
• Functional gains visible in work, relationships or daily life management

After stabilisation, ongoing monitoring moves to an individualised schedule, with heart rate and blood pressure checked at least every 6 months. The Vyvanse and Concerta product information both require at least an annual review to confirm treatment is still needed, and that review includes a broader assessment of ADHD symptom management and any emerging comorbidities.

This page is general information about ADHD medication in Australia, not advice about your individual treatment. Do not start, stop or change a dose without talking to the clinician who prescribed it. If you experience chest pain, fainting, or thoughts of self-harm, contact your prescriber or call emergency services on 000.

Frequently asked questions

Where GPs can prescribe ADHD medication, state by state
Find a GP who assesses ADHD in your state

Sources

• TGA Product Information: Vyvanse, lisdexamfetamine dimesilate (Takeda Pharmaceuticals Australia), TGA eBS document CP-2013-PI-02051-1, PI V12.0 (CCDS V40), read directly on TGA eBS 4 September 2026
• TGA Product Information: Aspen Dexamfetamine, dexamfetamine sulfate (Aspen Pharmacare Australia), TGA eBS document CP-2023-PI-02524-1, read directly on TGA eBS 4 September 2026
• TGA Product Information: Concerta, methylphenidate hydrochloride (Janssen-Cilag), TGA eBS document CP-2009-PI-00919-3, API v3.0, read directly on TGA eBS 4 September 2026
• TGA Product Information: Ritalin and Ritalin LA, methylphenidate hydrochloride (Novartis Pharmaceuticals Australia), TGA eBS document CP-2010-PI-03175-3, read directly on TGA eBS 4 September 2026
• AADPA Australian Evidence-Based Clinical Practice Guideline for ADHD, First Edition, October 2022, Summary of Recommendations (adhdguideline.aadpa.com.au, recommendations 5.1.5, 5.7.5 and 5.7.7, read 4 September 2026)
• Adler LA, Goodman DW, Kollins SH, et al. Double-blind, placebo-controlled study of the efficacy and safety of lisdexamfetamine dimesylate in adults with attention-deficit/hyperactivity disorder. Journal of Clinical Psychiatry. 2008;69(9):1364-1373. PMID 19012818
• TGA Australian Register of Therapeutic Goods (ARTG), tga.gov.au/resources/artg (search not independently completed this session; see verification file)