Yes, as long as they are derived from hemp, not marijuana, and contain less than 0.3% THC. No medical marijuana card is required to purchase or use hemp-derived CBD products.
Most drug tests screen for the psychoactive compound THC, not CBD. However, full-spectrum hemp extracts may contain trace amounts of THC, so could cause a positive result when screening urine and blood specimens, especially when taken at high doses.
An effective dosage can range from as little as 5mg of CBD per day and can go up to 150mg per day. Be sure to start low, and go slow. Take a few small doses over the course of the day, rather than one big dose. Use the same dose for several days, observe the effects, and, if necessary, adjust the amount.