How Do Paxil and Zoloft Work?
Paxil (paroxetine) and Zoloft (sertraline) are both selective serotonin reuptake inhibitors (SSRIs) that treat depression, anxiety disorders, OCD, PTSD, and panic disorder by blocking serotonin reuptake in the brain to boost its levels.[1][2]
Key Chemical and Dosing Differences
Paroxetine is a hydrochloride salt with a half-life of 21 hours, taken once daily at 20-60 mg for depression. Sertraline is a hydrochloride with a 26-hour half-life, dosed at 50-200 mg daily. Paroxetine has stronger anticholinergic effects, leading to more sedation and dry mouth; sertraline is less sedating and better for those needing daytime alertness.[1][3]
Common Side Effects Comparison
Both cause nausea, sexual dysfunction, and insomnia, but differences stand out:
| Side Effect | Paxil (Higher Risk) | Zoloft (Lower Risk) |
|-------------------|---------------------|---------------------|
| Weight gain | Common | Less common |
| Sexual issues | High (up to 70%) | Moderate (up to 60%) |
| Withdrawal symptoms | Severe ('discontinuation syndrome') | Milder |
| Sedation | Frequent | Rare |
Paxil's withdrawal hits harder due to its shorter effective duration after stopping.[1][2][4]
When Doctors Pick One Over the Other
Zoloft is often first-line for OCD and PTSD due to stronger evidence there. Paxil suits severe anxiety with insomnia but gets avoided in pregnancy (category D vs. Zoloft's C) and early breastfeeding over cardiac risks in newborns. Sertraline has fewer drug interactions, especially with tamoxifen.[3][5]
Withdrawal and Long-Term Use
Paxil requires slow tapering (over weeks) to avoid dizziness, flu-like symptoms, or 'brain zaps.' Zoloft allows faster stops with milder effects. Both carry black-box warnings for suicidality in young adults.[1][4]
Generic Availability and Cost
Both are off-patent generics. Monthly costs: $10-30 for either without insurance. No current patents block competition.[1][6]
[1]: FDA Label - Paxil
[2]: FDA Label - Zoloft
[3]: UpToDate - SSRI Comparison
[4]: American Family Physician - SSRI Discontinuation
[5]: NEJM - SSRIs in Pregnancy
[6]: Drugs.com - Pricing