Morning sickness typically starts around the 4th to 6th week of pregnancy and usually goes away by the end of the first trimester, around weeks 12 to 16. Most people experience the worst symptoms around weeks 8 to 10, after which the nausea and vomiting gradually subside. For some, it may last slightly longer, up to around 16 to 20 weeks, and in rare cases, it can persist throughout pregnancy. Severe cases may require medical attention, but for most, morning sickness improves as hormone levels stabilize and the placenta takes over hormone production.