Adult ADHD medication side effects — what to expect.

Stimulants (methylphenidate and dexamfetamine, including lisdexamfetamine) are first-line medication for adult ADHD where treatment is indicated and tolerated. Non-stimulant options (atomoxetine, guanfacine) are used where stimulants aren't suitable. This article is a general explainer about common side effects — it isn't medical advice and isn't a substitute for the prescribing conversation with your psychiatrist.

Common, usually mild and short-lived

Most adults starting stimulant ADHD medication notice one or more of the following in the first one to four weeks. These usually settle as the body adjusts, or with a dose or timing change discussed with your prescriber:

• Reduced appetite — particularly around the middle of the day. Often manages with a bigger breakfast, an evening 'second dinner', and protein-heavy snacks.
• Difficulty getting to sleep — usually when the dose is taken too late in the day, or the dose is too high.
• Dry mouth.
• Mild headache for the first few days.
• A brief 'come-down' as the medication wears off — often a low or tired hour in the late afternoon.
• Slight increase in heart rate and blood pressure — your psychiatrist will monitor this.

Less common but worth telling your prescriber about

• Feeling 'wired', anxious or irritable rather than calmer and more focused — often a sign the dose is too high.
• Significant weight loss over weeks to months.
• New or worsening anxiety or panic symptoms.
• Persistent insomnia despite dose-timing changes.
• Tics, jaw-clenching, or repetitive movements.
• Mood swings or low mood in the late afternoon/evening 'come-down'.

These don't necessarily mean stopping the medication — but they do mean a conversation. Most can be managed with dose, timing, formulation or medication changes.

Reasons to call your prescriber promptly

• Chest pain, palpitations or fainting.
• Severe headache that doesn't settle.
• Marked changes in mood, including new thoughts of self-harm.
• Visual or perceptual changes.
• Signs of an allergic reaction — rash, swelling, breathing difficulty.

Non-stimulant medication

Atomoxetine and guanfacine are non-stimulant options. They have a different side-effect profile — they take longer to reach full effect (often four to eight weeks), and common early side effects include drowsiness, low energy, gastrointestinal upset and (for atomoxetine) appetite and sleep changes. Your psychiatrist will explain monitoring and what to watch for if either is being considered.

What monitoring looks like in Australia

Best-practice ADHD prescribing in Australia (consistent with AADPA's evidence-based guideline) includes baseline measurements (blood pressure, heart rate, weight), regular review in the first few months of treatment, and at least annual review once dosing is stable. Most SetMind patients have a structured shared-care plan with their GP so day-to-day prescribing and monitoring stays local, with specialist review at agreed intervals.

Questions worth asking your psychiatrist

1. What dose are we starting at, and how will we know it's working?
2. What side effects should I expect in the first month, and which ones should I call about?
3. What's the plan if the first medication doesn't suit me?
4. How will my GP and I manage monitoring once we're stable?
5. Are there any of my current medications I should flag for interactions?