Antidepressants are the most prescribed treatment for depression anywhere in the world. The research showing they work looks impressive at first glance. Then you check what the patients were being compared against, and the picture gets a lot more interesting.
📚 What you need to know
Biological treatments aim to treat disorders such as MDD by targeting brain chemistry.
Antidepressants are the most widely prescribed drug therapy for MDD.
SSRIs prevent reuptake of serotonin into the presynaptic neuron, increasing serotonin in the synaptic cleft. Examples: fluoxetine, citalopram.
SNRIs work similarly but also increase noradrenaline. Examples: duloxetine, venlafaxine.
Both rest on the monoamine hypothesis: low or irregular serotonin is linked to depressive symptoms.
Kroenke et al. (2001) is your study — check carefully what it compared.
Concept links: responsibility (root causes and side effects) and change.
Two families of antidepressant
You only need to be able to tell them apart and say what each blocks.
If you can already draw the synapse from the neurotransmitters page, you can explain both of these in two sentences. It is the same mechanism, applied to one chemical or two.
SSRIs restore balance by keeping more serotonin available in the synapse, preventing serotonin molecules from being absorbed back into the presynaptic neuron. That is the whole argument for the monoamine hypothesis in one sentence — and it is also, as we saw earlier, the point where the reasoning gets shaky.
🔬 Kroenke et al. (2001)
Comparing three SSRIs over nine months
AIM
To compare the effectiveness of three SSRIs — paroxetine, fluoxetine and sertraline — in treating MDD.
PARTICIPANTS
573 patients with MDD from 37 clinics across the USA. 84% Caucasian, 13% Black, 3% other; 79% female, 21% male; aged 19 to 96 with a mean age of 46. All had been clinically recommended for SSRI treatment.
PROCEDURE
Participants completed a baseline assessment over the telephone and were randomly assigned to one of the three SSRIs, roughly 190 per group. Treatment lasted 9 months. At 1, 3, 6 and 9 months each participant completed a Mental Component Summary Score (MCSS) scale with 36 items measuring MDD symptoms, plus self-reports on social and work functioning, physical health, sleep, memory and pain.
RESULTS
79% completed the full 9-month programme. Participants improved similarly across all three SSRIs, with a 15 to 17 point improvement on the MCSS. Depressive symptoms decreased from 74% at baseline to 32% at 3 months and 26% at 9 months.
CONCLUSION
SSRIs are effective in treating MDD, and the three drugs show similar levels of effectiveness.
The drop is real and large. What the design cannot tell you is how much of it came from the drug, how much from time passing, and how much from being cared for by a clinic for nine months.
This is the point almost every student misses, so make it yours. Kroenke compared three SSRIs against each other. There was no placebo group and no no-treatment group. That design can prove the three drugs are equally effective — which is exactly what the conclusion says. It cannot prove any of them beat doing nothing. Getting that distinction right is worth more than memorising the numbers.
Two other things worth noticing
The drop happened early. Symptoms fell from 74% to 32% in the first three months, then barely moved for the next six. Most of the change happened fast and then plateaued.
21% dropped out. Only 79% completed the programme. The people who stayed may have been the ones it was working for, which would make the results look better than they are.
Evaluating drug therapy for MDD
Strengths
Limitations
Reduced hospitalisation. Antidepressants let many people manage symptoms outside hospital, giving them more freedom and autonomy.
There is real debate over effectiveness — some clinicians argue the effects may be little better than a placebo.
Drug therapy is generally cheap and widely available, unlike CBT, which needs trained therapists, takes longer and often involves long waiting lists.
There is uncertainty about the monoamine hypothesis itself, as depression is likely a cluster of disorders with multiple underlying biological and psychological factors.
Kroenke used random assignment across 37 clinics, which improves reliability and generalisability within the USA.
No placebo or control group, so the size of the drug effect cannot be isolated.
Standardised measurement using the MCSS makes results comparable between patients.
The sample was 79% female and 84% Caucasian, limiting generalisability.
Linking to the concepts
Responsibility: drug therapy can be effective, but it does not address the root causes of MDD. It holds the symptoms at bay, with the possibility that the disorder may recur later. Antidepressants can also have side effects, since they act directly on the brain, so the attending clinician should monitor the patient for harmful consequences.
Change: MDD is not a stable, unchanging condition — it fluctuates over time. Life events, hormonal changes and illnesses can bring it on or help lift it. Drugs may suit someone at one point in their life but not every time they experience symptoms. That is why the whole person should be considered when prescribing, rather than taking the biologically reductionist route every time.
EXAM ANSWER
Evaluate one biological treatment for one disorder. [22 marks]
Explain the treatment mechanically
SSRIs block the reuptake pump, so serotonin stays in the synaptic cleft longer. SNRIs do the same for noradrenaline too.
Evidence
Kroenke et al.: 573 patients, symptoms falling from 74% to 26% over 9 months, with all three SSRIs performing similarly.
Strength that is about people, not chemistry
Cheap, widely available, and it keeps people out of hospital with more autonomy — unlike CBT with its waiting lists.
The methodological hitNo placebo group, plus 21% attrition, so the true size of the effect is unknown.
Conclude: effective and accessible, but symptom management not cure“holds symptoms at bay” is the phrase that captures the responsibility concept
💡 Exam tips
Name two drugs from each family. Specific examples are quick credit.
Say what Kroenke actually compared before you evaluate it. Design first, then criticism.
Use the placebo debate as your main limitation — it is in the syllabus and it is genuinely strong.
The comparison with CBT (cost, waiting lists, trained staff) works in both directions. Reuse it later.
Attrition of 21% is a methodological point most candidates never make.
Cross-link to the neurotransmitters page for the mechanism, so you are not describing the synapse twice from scratch.
⚠ Common mix-ups
Saying the study proved SSRIs beat placebo. There was no placebo group.
Saying SSRIs “increase serotonin production”. They block reabsorption of what is already there.
Confusing SSRI and SNRI. The extra N is noradrenaline.
Reading 26% as 26% improved. It is the proportion still showing depressive symptoms at 9 months.
Treating drug therapy as a cure. It manages symptoms; MDD may recur.
Forgetting side effects. They are central to the responsibility concept.
Up next: Drug Treatments for Nicotine Addiction — a completely different chemical target, and a statistic that is misread more often than any other in this option.
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