Shares of Youngevity International Inc. (NASDAQ: YGYI) were down 23.5% as of 10:56 a.m. EDT on Wednesday. There was no news from the California-based multilevel marketer. So why did Youngevity's share price tank?Perhaps the best explanation is that when major marijuana stocks sneeze, Youngevity catches a cold. Several large marijuana stocks tumbled on Wednesday as the Canadian recreational marijuana market opened for business for the first time.