Fluoxetine

Is fluoxetine safe?

For most adults and many teenagers, yes, with monitoring. Fluoxetine, sold as Prozac, was the first selective serotonin reuptake inhibitor (SSRI) approved in the US, cleared at the end of 1987. Almost four decades of use have shown it is not addictive and is far less dangerous in overdose than the tricyclic antidepressants it replaced.

Its defining feature is how long it stays in the body. That cuts both ways: missed doses and stopping matter less, but interactions and side effects can last for weeks after the last capsule. We score it 70, just below sertraline at 72, mainly because of its interactions and a less forgiving overdose record.

A drug that stays for weeks

With regular use, fluoxetine has a half-life of 4 to 6 days, and its active metabolite norfluoxetine 4 to 16 days. Most SSRIs clear in a day or two. The Prozac label spells out what that means in practice:

• dose changes take several weeks to show their full effect
• an MAOI antidepressant must not be started until at least 5 weeks after fluoxetine stops, against 14 days for most SSRIs
• thioridazine needs the same 5-week gap
• drugs broken down by the liver enzyme CYP2D6CYP450 enzymesA family of liver enzymes that break down many medicines. When another drug or supplement speeds them up or slows them down, drug levels change.More in the glossary can stay raised for weeks after fluoxetine is stopped

The upside is that levels fall slowly when treatment ends. Discontinuation symptoms such as dizziness, irritability and electric-shock sensations still happen with SSRIs, but fluoxetine is the one prescribers often use to make stopping easier.

Side effects in the first weeks

In the label's pooled depression trials (1,728 people on fluoxetine, 975 on placebo):

Side effect	Fluoxetine	Placebo
Nausea	21%	9%
Insomnia	16%	9%
Somnolence	13%	6%
Anxiety	12%	7%
Reduced appetite	11%	2%
Tremor	10%	3%

Fluoxetine is more activating than some SSRIs, which is why the label recommends taking it in the morning. Sexual side effects, including delayed orgasm and lower libido, are common to the class and are often under-reported. Rarer but serious risks include low blood sodium in older people, triggering of mania in undiagnosed bipolar disorder, angle-closure glaucoma and, in post-marketing reports, QT prolongationQT prolongationA delay in the heart's electrical recovery between beats, seen on an ECG. Some medicines cause it, and in rare cases it leads to a serious heart rhythm problem.More in the glossary and torsade de pointes.

The boxed warning

Like every antidepressant in the US, fluoxetine carries a boxed warningBoxed warningThe strongest safety warning the US FDA puts on a medicine's label, printed inside a black border at the top.More in the glossary that it raised suicidal thoughts and behaviour in children, teenagers and young adults in short-term trials, with no rise over 24 and a fall over 65. It is still the antidepressant with the most evidence in young people. In the UK it is the only one licensed for depression in 8 to 18 year olds, and NICE recommends it alongside talking therapy when therapy alone has not worked.

Pregnancy is a live question. The MHRA reported a possible small increase in heart defects with first-trimester use in 2014, and the label notes risks to the newborn and of bleeding after birth. A 2025 citizen petition asked the FDA to add a pregnancy boxed warning to SSRIs; it was still pending in early 2026, and the January 2026 Prozac label has no such warning. Untreated depression also carries risks, so do not stop fluoxetine on your own if you become pregnant.

Overdose

Fluoxetine alone rarely kills, but it is not as benign as sometimes claimed. The older label recorded 633 adult overdoses on fluoxetine alone up to 1999: 34 died, 378 recovered fully and 206 had an unknown outcome. One person survived 8 g. The current label warns that seizures and heart rhythm problems can appear hours later, so anyone who has taken too much needs hospital assessment even if they feel fine. In the US call Poison Control on 1-800-222-1222; in the UK call 111 or 999.

Interactions to check

The label contraindicates MAOIs, linezolid, intravenous methylene blue, pimozide and thioridazine. Tramadol, triptans, other antidepressants, lithium and St John's wort raise the risk of serotonin syndromeSerotonin syndromeA reaction caused by too much serotonin in the body, usually from combining medicines that raise it. Symptoms range from shivering to high fever.More in the glossary. Our 5-HTP page covers the same risk with that supplement. Fluoxetine strongly blocks CYP2D6CYP450 enzymesA family of liver enzymes that break down many medicines. When another drug or supplement speeds them up or slows them down, drug levels change.More in the glossary, which can push up levels of tricyclic antidepressants, some antipsychotics and beta blockers such as metoprolol, and the NHS lists tamoxifen among the medicines to check. With warfarin, apixaban, aspirin or ibuprofen, bleeding risk rises.

Doses

Use	Adult start (US label)	Range
Depression	20 mg each morning	20 to 80 mg a day
OCD	20 mg each morning	20 to 60 mg, up to 80 mg
Bulimia	60 mg each morning	60 mg
Panic disorder	10 mg a day	Raised to 20 mg after a week

Older people, those with liver problems and people on many medicines get lower or less frequent doses. Children usually start on 10 mg.

Who should be careful

Talk to your doctor or pharmacist before starting fluoxetine, or before adding anything to it, if you are under 25, have bipolar disorder or have had mania, have a heart rhythm problem or take a QT-prolongingQT prolongationA delay in the heart's electrical recovery between beats, seen on an ECG. Some medicines cause it, and in rare cases it leads to a serious heart rhythm problem.More in the glossary drug, take a blood thinner, tamoxifen or another antidepressant, have epilepsy, or are pregnant or breastfeeding. Tell anyone prescribing for you in the weeks after you stop, because it is still in your system.

How we scored it

Track record (94) and dependence (86) are the strongest factors. Interactions (52) are weaker than for sertraline because of the CYP2D6CYP450 enzymesA family of liver enzymes that break down many medicines. When another drug or supplement speeds them up or slows them down, drug levels change.More in the glossary effect and the 5-week washout, regulatory warnings (50) reflect the boxed warningBoxed warningThe strongest safety warning the US FDA puts on a medicine's label, printed inside a black border at the top.More in the glossary, and overdose marginOverdose marginHow far a normal dose is from a harmful one. A wide margin means an accidental extra dose is unlikely to cause serious harm.More in the glossary (75) the heart and seizure risks.