Prolonged exposure to 1.5Gs isn't lethal, but women are recommended to use sports bras, and men to wear supportive underwear (jockeys/briefs), lest certain tender bits get sore. There'd be a DX penalty - reflexes are adjusted for things falling more slowly, and trips and sprains become more common. Everyone will feel like overweight old people ;) Given prolonged exposure (months), people bulk up and adjust, and have no long-term ill effects beyond higher blood pressure.
At 2G, definitely support garments. Trips become sprains, sprains become damaged joints or broken bones. Blood pressure issues become serious - people faint when they stand up due to blood flow issues. Bed sores are common for people who don't move around in their sleep. Pregnant women have significant risks, and need to spend the last trimester sitting & lying. Tolerable - especially by fit people for days at a time - but not recommended.
And BirdOfPrey, exactly!
Put it this way - the VASIMR drive promises 0.1G continuous accelleration. It can't lift off Earth, but it turns a 9 month Hohman transfer orbit (unpowered) into 2 weeks to Mars under power. The SRB boosts the shuttle at - what, 3-4G - but burns out tout suite.