Yes and no, but mostly no. Some chemicals are more fat soluble and distribute into our fat stores. Medications with this property include amiodarone and azithromycin -- we typically administer a large loading dose up front to saturate the fat compartment, otherwise we wouldn't be able to attain appropriate levels in the blood. These medications are expected to wash out over time after you stop taking them. This has nothing to do with losing weight, it's just concentration gradients.

Fyi this is why it can take weeks to clear cannabis on a urine test.