Has anyone compared Qsymia and Xenical in the same trial?

No head-to-head trial has compared these two drugs. Qsymia's figures come from CONQUER (56 weeks) and Xenical's from Sjostrom 1-year RCT (52 weeks), which enrolled different people for different lengths of time. Numbers from separate trials can be read side by side, but they are not a measured difference.

What does each one cost per month?

Qsymia is listed at $30–$400/month (generic; brand runs to $400). Xenical is listed at $40–$400/month (over-the-counter strength; prescription runs to $400). The full price note for each is set out in the cost section above. What you pay depends on your insurance, your dose and your pharmacy.

Can I switch from Qsymia to Xenical?

Switching between weight-loss medicines is a decision for the prescriber who knows your history, your other medicines and how you have responded so far — this site cannot make it for you. What switching involves in practice, including dose steps and the gap between drugs, is set out on the switching page.

Which side effects were reported most often?

In CONQUER (56 weeks), the reaction reported most often with phentermine / topiramate ER was dry mouth — 21% of participants. In XENDOS (208 weeks), the reaction reported most often with orlistat was oily/fatty stools (steatorrhoea) — 27% of participants. Rates come from different trials with different participants, and a rate is not a prediction for any one person.

Qsymia vs Xenical: trials compared

At a glance

Qsymia and Xenical compared on form, trial results, cost and reported side effects
	Qsymia	Xenical
Form	Daily capsule	3x daily with meals
How often	Daily oral capsule — no injection	Three capsules daily, taken with each fat-containing meal
Weight loss in trials	Up to 9.8% — CONQUER (56 weeks)	Up to 8.5% — Sjostrom 1-year RCT (52 weeks)
FDA approved	2012	1999
Made by	Vivus	Roche (Xenical) / GSK (Alli OTC)
How it works	Phentermine suppresses appetite by triggering the release of adrenaline-like chemicals in the brain's hunger control centre.	Blocks pancreatic lipase enzymes in the small intestine, preventing approximately 30% of dietary fat from being broken down and absorbed.
Monthly cost, self-pay	$30–$400/mogeneric; brand runs to $400	$40–$400/moover-the-counter strength; prescription runs to $400
Most reported reaction	Dry mouth 21% (CONQUER)	Oily/fatty stools (steatorrhoea) 27% (XENDOS)

Every figure in this table is read from the same trial and label records used everywhere else on this site.

Weight loss in each drug's main trial

No head-to-head trial has compared these two drugs.

Qsymia(phentermine / topiramate ER)9.8%

CONQUER (56 weeks)

Xenical(orlistat)8.5%

Sjostrom 1-year RCT (52 weeks)

In clinical trials, participants taking phentermine / topiramate ER lost on average up to 9.8% of their starting body weight, and participants taking orlistat lost on average up to 8.5%. Those numbers come from two different studies: CONQUER enrolled 2,487 adults with obesity and at least 2 weight-related health conditions over 56 weeks against placebo, while Sjostrom 1-year RCT enrolled 743 adults with obesity over 1 year (52 weeks) against placebo. Who took part, how long each trial ran and what each drug was measured against all move the percentage, so the two figures are not a measured difference between the drugs.

Monthly cost, self-pay

The bar spans the range in each drug's price record — lowest listed price to highest.

Qsymia$30–$400/mo

generic; brand runs to $400

~$30–$80/month generic; ~$200–$400/month brand (Qsymia).

Xenical$40–$400/mo

over-the-counter strength; prescription runs to $400

Prescription Xenical ~$200–$400/month; over-the-counter Alli (60mg) ~$40–$60/month.

Self-pay prices are what the manufacturer or the pharmacy lists, not what most people end up paying. Qsymia: $30–$400/month. Xenical: $40–$400/month. Insurance, dose and pharmacy all change both figures.

Side effects reported in the trials

CONQUER and XENDOS did not report the same reactions, so there is no shared row to line up. Each drug's own reported rates are listed below.

Qsymia

Paraesthesia (tingling in hands/feet)20%
Dry mouth21%
Constipation17%
Insomnia10%
Dizziness9%
Cognitive effects ('brain fog')8%

From CONQUER

Xenical

Oily/fatty stools (steatorrhoea)27%
Faecal urgency22%
Oily spotting on underwear27%
Faecal incontinence8%
Abdominal pain/discomfort14%

From XENDOS

A rate is the share of trial participants who reported that reaction, not a prediction for any one person.

How they differ in practice

How you take it

Qsymia — Once-daily extended-release capsule
Xenical — Oral capsule 120 mg, three times daily with meals (prescription). Also available OTC as Alli at 60 mg.

Dose build-up

Qsymia — 3.75/23 mg → 15/92 mg, titrated over 14 weeks

Where a drug is not listed here, its prescribing information sets out its own dose steps.

How soon it acts

Qsymia — Appetite suppression typically begins within the first week; significant weight loss by 12–16 weeks
Xenical — Weight effects begin from the first week (related to calorie malabsorption), but significant loss takes 8–12 weeks

Heart and metabolic findings

Qsymia — In CONQUER, significant reductions in blood pressure, waist circumference, triglycerides, and blood glucose were observed.
Xenical — In the 4-year XENDOS trial, orlistat reduced progression from prediabetes to type 2 diabetes by 37% compared to placebo plus lifestyle changes.

As stated in each drug’s trial record — not a claim about which drug protects the heart more.

Other findings recorded

Qsymia — Generic now available (from 2025) — significantly lower cost than GLP-1 drugs; improved blood pressure and triglycerides in CONQUER trial
Xenical — 37% reduction in progression to type 2 diabetes (XENDOS, 4 years); only approved obesity drug with a 4-year safety dataset

If you stop taking it

Qsymia — Weight regain after stopping is expected.
Xenical — Weight is typically regained after stopping.

Common questions

Written and maintained by one person · Built with agentic AI tools · Every number checked against the cited trial · Not medical advice

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Qsymia — results, side effects, cost and how it is taken

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Xenical & Alli — results, side effects, cost and how it is taken

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Last reviewed: September 2026

Medical disclaimer: This website is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any treatment.