Mental Health Medication Side Effects

Mental health medicines cover several very different groups, and their side effects differ accordingly. What they share is a pattern worth knowing before you start: side effects usually appear before the benefit does. Most take two to six weeks to work properly, while the unwanted effects often show up in the first days, so the early period can feel like all cost and no return. Knowing that in advance is one of the more useful things about starting treatment.

The other thing they share: none of them should be stopped abruptly.

Common side effects and early adjustment effects

Antidepressants (SSRIs and SNRIs). Nausea, headache, sleep changes, sweating, and increased anxiety in the first week or two. Most settle within a month. See antidepressant side effects and SSRI side effects.
Antipsychotics. Drowsiness, dizziness on standing, weight gain and metabolic change; movement effects with some. See antipsychotic side effects.
Mood stabilisers. Tremor, thirst, weight change and digestive effects; several need blood monitoring. See mood stabiliser side effects.
Sedatives and sleeping tablets. Drowsiness, next-day impairment, and dependence with regular use. See sleeping tablet side effects.

Many early effects are dose-related and improve with time, a dose adjustment, or a change in when the dose is taken. That middle ground between enduring it and stopping is the reason to raise things rather than decide alone. See drowsiness on mental health medication.

Serious mood, behaviour or physical symptoms to take seriously

New or worsening thoughts of self-harm or suicide. Risk is highest in the first weeks and after any dose change, and is of particular concern in people under 25. Contact a doctor or emergency services urgently. Telling someone close to you what to watch for when you start is worth doing.

Get emergency help for:

Agitation or confusion with fever, sweating, a racing heart and muscle twitching, which can indicate serotonin syndrome
High fever with marked muscle stiffness and confusion, which can indicate a rare reaction to antipsychotics
A rash that blisters or peels, or swelling of the face or throat
Fainting, or a fast or irregular heartbeat
Seizures, or severe confusion

Contact your prescriber promptly for: new involuntary movements, particularly of the face or tongue; a switch into unusually elevated mood with reduced need for sleep; unexplained bruising or bleeding; marked thirst with frequent urination; or fever with a sore throat and mouth ulcers. See when to call a doctor.

Sexual, sleep, weight and emotional side effects

These four are grouped together because they share a problem: they are the effects people are least likely to mention, and among the most likely to lead someone to stop treatment quietly rather than discuss it.

Sexual side effects are common with SSRIs and often persist rather than fading. They are also among the most actionable, since a dose change or switch may help. See SSRI sexual side effects.
Weight gain is most associated with several antipsychotics and some mood stabilisers, and is easier to address early. See mental health medication and weight gain.
Sleep can be disturbed in either direction, and dose timing can often be adjusted.
Emotional blunting. Feeling flattened or less able to feel strong emotion, including positive ones. This is frequently mistaken for continuing illness when it may be a dose effect. See emotional numbness on antidepressants.

None of these are trivial, and none are things you should simply accept as the price of treatment.

Interactions, alcohol, pregnancy and other risk factors

Alcohol. Adds to drowsiness and can worsen low mood. See mental health medication and alcohol.
St John’s Wort. Should not be combined with antidepressants. See supplements with antidepressants.
Anti-inflammatories. Add bleeding risk alongside SSRIs.
Tramadol and migraine triptans. Raise serotonin syndrome risk.
Pregnancy and breastfeeding. Needs individual discussion weighing treated against untreated illness. Do not stop on discovering a pregnancy without advice. See mental health medication in pregnancy.
Age. Older adults are more sensitive to sedation, falls and low sodium; effects in teenagers need closer monitoring. See older adults and teens.

What to ask your doctor before changing dose or stopping

Do not stop abruptly. Antidepressants can cause discontinuation symptoms, dizziness, electric-shock sensations, irritability and flu-like feelings. Antipsychotics and mood stabilisers carry relapse risk. Benzodiazepines and sleeping tablets can cause severe withdrawal. None of this is addiction in the ordinary sense, but all of it is avoidable with a planned reduction. See should I stop my mental health medication.

How long before I should expect benefit, and what should I expect before then?
Which symptoms mean I should contact you rather than wait?
What monitoring do I need, and when?
What can be done about sexual side effects or weight change?
If I want to stop eventually, how would we do it?

Related mental health medication guides

Medical Disclaimer: This content is for informational and educational purposes only and does not constitute medical diagnosis, prescription, or professional advice. Always read the patient information leaflet and consult a qualified doctor or pharmacist regarding any medicine or health concern.