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What to do if…
you start a new medicine and feel faint, unusually restless, or severely sweaty

Short answer

Treat this as potentially urgent: sit or lie down safely and get same-day advice. If you have any signs of a severe allergic reaction or you collapse, call 999.

Do not do these things

  • Do not drive, cycle, or “push through it” to get somewhere while you feel faint or unsteady.
  • Do not take another dose “to see if it settles” until you’ve checked what to do with a clinician or pharmacist.
  • Do not suddenly stop a prescribed medicine without advice unless you’re being told to by an emergency clinician (some medicines need tapering).
  • Do not drink alcohol or take recreational drugs “to calm down” — it can worsen side effects and make it harder to assess what’s happening.
  • Do not stay alone if you feel like you might pass out, especially after a first dose or a dose increase.

What to do now

  1. Get into a safer position immediately.

    • If you feel faint: lie flat and, if you can, raise your legs on a cushion or chair.
    • If you’re short of breath: sit upright instead.
    • Loosen tight clothing and keep the room cool.

  2. Check for “call 999 now” signs (don’t wait for them to get worse). Call 999 if you have any of these, especially soon after taking the medicine:

    • Trouble breathing, wheeze, tight throat, swelling of face/lips/tongue, widespread hives/rash
    • Collapsing, fainting that does not quickly improve when lying flat, severe confusion
    • Severe chest pain, new one-sided weakness, seizure, or blue/grey lips

  3. If you have an adrenaline auto-injector and you think this is anaphylaxis: use it and call 999.
    Say “anaphylaxis” when you call. If symptoms are not improving after about 5 minutes, or they improve and then return, and you have a second auto-injector, use it (follow your device instructions).

  4. If you are stable but still feel faint/restless/severely sweaty, get urgent advice today via NHS 111.

    • 111 online is generally for people aged 5 and over.
    • Call 111 if it’s for a child under 5, or if you cannot use the online service.
      Tell them: the medicine name/strength/dose, when you took it (and if it was a first dose or dose increase), your symptoms, and any other medicines/supplements you’ve taken.

  5. Speak to a pharmacist the same day if you can’t reach the prescriber quickly.
    Ask specifically: “Should I take my next dose?” and “Could this be a serious reaction or interaction with my other medicines?”

  6. If you have diabetes or are prone to low blood sugar, check it.
    Treat low glucose as you’ve been advised to, and still seek advice if symptoms persist or you’re unsure.

  7. Write down a quick “symptom timeline” now.
    Note the time you took the medicine, when symptoms started, and any changes. Keep the packaging/leaflet handy — this helps 111/clinicians decide faster.

What can wait

  • You do not need to decide today whether you’ll keep taking the medicine long-term — the priority is safety and getting the right immediate advice.
  • You do not need to diagnose the cause (side effect vs. allergy vs. interaction) right now.
  • You can report suspected side effects later; first focus on getting assessed/triaged.

Important reassurance

Feeling faint, unusually agitated/restless, or drenched in sweat after starting a new medicine can be frightening, and it’s reasonable to treat it as urgent. Many reactions are manageable once a clinician knows exactly what you took and what you’re feeling — the key is not being alone with it and not taking extra doses until advised.

Scope note

This is first-steps-only guidance for the first hours/day after symptoms start. Medication reactions and interactions can be complex, so same-day clinical triage is often the safest next move.

Important note

This is general information, not a diagnosis or a substitute for medical care. If you feel you might collapse, you’re struggling to breathe, or symptoms are rapidly worsening, call 999.

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