I'd avoid it. Tramadol is one of the more problematic drugs to combine with sertraline, for a few reasons:
**Serotonin syndrome.** Tramadol isn't just an opioid — it also blocks serotonin and norepinephrine reuptake. Stacking it on 100 mg of sertraline meaningfully raises the risk of serotonin toxicity: agitation, confusion, sweating, tremor, muscle twitching or stiffness, overactive reflexes, diarrhea, racing heart, fever. It can come on within hours of a dose and, in severe cases, is a medical emergency.
**Seizures.** Tramadol lowers the seizure threshold on its own, and SSRIs add to that. Seizures have happened at ordinary doses in people on this combination.
**It may not even work well.** Tramadol is a prodrug — the liver enzyme CYP2D6 has to convert it into the metabolite that actually relieves pain. Sertraline inhibits that enzyme, so you can end up with less pain relief while the parent drug (the part driving the serotonin and seizure risk) builds up. Worst of both worlds.
There's also the separate issue that a friend's leftover opioid isn't a known quantity — dose, strength, whether it's what they think it is.
**What actually works better for dental pain:** ibuprofen 400 mg plus acetaminophen 500–1000 mg taken together, every 6 hours. In head-to-head trials for acute dental pain this combination outperforms opioids, including tramadol. Check it's okay for you first (avoid ibuprofen with kidney disease, ulcers, blood thinners; keep acetaminophen under 3–4 g/day and lower if you drink regularly or have liver issues). Note that SSRIs plus NSAIDs do modestly raise GI bleeding risk, so take it with food and don't stretch it out for weeks.
**Get the tooth looked at.** Pain that bad usually means an infection or exposed pulp, and painkillers only mask it. Many dentists keep emergency slots. Go to urgent care or the ER instead if you have facial or jaw swelling, fever, difficulty swallowing or opening your mouth, or swelling spreading toward your eye or neck — that's a spreading infection, not just a toothache.
If you've already taken a dose and feel shaky, sweaty, agitated, or unusually twitchy, get seen the same day.