The Impact of State Medical Marijuana Laws on Infant Health

Medical marijuana use was first legalized in 1996, in the state of California. As of September 2015, medical marijuana has been legalized in 23 U.S. states and the District of Columbia. This along with the legalization of marijuana for recreational use in four U.S. states: Colorado, Washington, Oregon and Alaska. While several researchers have estimated the causal relationship between the medical marijuana laws (MMLs) and its recreational use, no consistent conclusion is reached so far. Wen et al. (2012) showed that the adoption of MMLs in seven states during 2004-2011 increased the probability of marijuana initiation, its use and dependence, and also lead to an increase in binge drinking. A few other studies (for example, Cerdá, et al., 2012; Wall et al., 2011) also provide evidence that states with MMLs have higher rates of marijuana use, but these studies do not focus on a causal relationship. Meanwhile, some researchers fail to find a statistically significant effect of MMLs on marijuana use (for example, Khataphoush, 2004; Harper, 2012; Lynne-Landsman, 2013; Anderson, 2015).

As legislation on marijuana becomes more lenient, there is an increasing interest to monitor the effect of these policies on public health outcomes. As of now, there is no knowledge of the impact of the MMLs on infant health. In the U.S., marijuana is the most frequently used illicit drugs during pregnancy. Currently, about 5.2% of women smoke marijuana during pregnancy, which is equivalent to approximately 115,000 pregnant women annually (Warner et al., 2014). In 2013, about 16.5% of adolescents reported marijuana use during pregnancy, which more than doubles the rate for mothers aged 18 to 25 (7.5%). Prenatal use of marijuana has been documented to be associated with infertility, pregnancy-related complications, and adverse infant health outcomes. In particular, women who used marijuana during pregnancy are more likely to have shorter gestation period and low birth-weight infants than those who did not (Cornelius et al., 1995; EI-Mohandes et al., 2003; Hayatbakhsh et al., 2011). These adverse birth outcomes not only lead to a higher risk of infant mortality and morbidity, but also have longer-term negative impacts on both child development and adult health.

The adoption of MMLs may not only increase marijuana use, but also raise the consumption of other illicit drugs, alcohol and tobacco among pregnant women. All of these substance use will lead to adverse infant health. Therefore, any effect or even none at all of the medical marijuana would be of notable interest to policy makers. Using individual-level birth certificate data from the Natality Detail File between 1993 and 2011, I estimate the effects of state marijuana legislation on infant mortality, birth weight, gestation, and pregnancy complication. My preliminary results indicate that the passage of medical marijuana law increases low birth-weight infants among teenage mothers, but has no statistically significant effects on adult mothers.