In a surprising, peer-reviewed study published last July in the scientific journal, Addiction, a trio of researchers from the Bixby Center for Global Reproductive Health discovered that alcohol use doubled the chances of unintended pregnancy, whereas cannabis use had no measurable impact.

The longitudinal study was based on an analysis of more than 2,000 patients receiving care between 2019 and 2022 at 23 primary and reproductive care facilities across five southwestern U.S. states. Patients were between the ages of 15 and 34, all capable of pregnancy, and none of them pregnant at the time of enrollment in the study.

The data involved self-reported cannabis, alcohol, and other drug use in the month prior, tracking every month for 13.5 months. Pregnancy status was assessed every six weeks. At baseline, patients had the following substance use profiles for the previous 30 days:

• 40% reported drinking heavily
• 13% reported cannabis use
• 3% reported using other drugs

Interestingly, people who reported heavy alcohol use or daily cannabis use had a higher-than-average desire to avoid pregnancy. This was measured using the Desire to Avoid Pregnancy scale, or DAP Scale, a 14-item questionnaire rated on a Likert scale that goes from zero to four:

0 – Strongly agree

1 – Agree

2 – Neither agree nor disagree

3 – Disagree

4 – Strongly disagree

Among those who drank heavily, the chance of unintended pregnancy doubled compared with those who did not drink. Among those who use cannabis daily, the chance of unintended pregnancy was exactly the same as that of those who did not use the drug. The researchers conclude:

Heavy drinking, but not cannabis use or other drug use, appears to be associated with elevated pregnancy risk among those who most desire to avoid pregnancy.

In many ways, the research corroborates an earlier study involving 1,115 patients, conducted by a group of researchers spread across the U.S. and published in the Journal of Women’s Health. A total of 15.5% of the women had a diagnosed substance use disorder (SUD), and more than half (61.1%) self-reported substance use in the previous 30 days.

The researchers concluded:

Women with prepregnancy substance use or SUD have decreased prevalence of well-timed and intended pregnancies.

However, the details show the picture is quite different between cannabis use disorder (CUD) and alcohol use disorder (AUD). Self-reported intended pregnancies were 13.1% with CUD and 46.8% with AUD. Here is how researchers explain these findings:

In adjusted models, women with any prepregnancy substance use were 15% less likely to report their pregnancy as happening at the right time and 20% less likely to report their pregnancy as intended compared with women with no substance use.

The study did not assess binge drinking, and had so few patients in the “other drugs” category besides marijuana and alcohol that they couldn’t get enough data to form conclusions. They did say “more than two times as many women with prepregnancy substance use and almost three times as many women with SUD also use tobacco,” pointing out a significant amount of polysubstance abuse.

Very few studies have assessed the impact of cannabis on unintended pregnancy rates. It is often merged with substance use disorder, even though the results are dramatically different between marijuana and alcohol. The data is so bad that one published systematic review found 97 full texts and only three met the criteria to be included in the scoping review. Their abrupt conclusion:

There is a paucity of data examining the intersection between AOD use [alcohol and other drug use] and UIP [unintended pregnancy] and further research is needed.

Yes, indeed. However, that research should be informed by the fact that the likelihood of unintended pregnancy for habitual cannabis users is half that for people with alcohol use disorder. Research into cannabis has been suppressed for decades. Now that it is being allowed, studies are showing the drug has benefits as well as problems caused by its abuse. We will follow the science here at AddictionNews.

Written by Steve O’Keefe. First published March 5, 2026.

Sources:

“Alcohol and drug use and attainment of pregnancy preferences in the southwestern United States: A longitudinal cohort study,” Addiction, July 30, 2025.

“Heavy Drinking Raises the Risk of Undesired Pregnancy; Cannabis Use Does Not,” Addiction Journal, July 31, 2025.

“Association of Prepregnancy Substance Use and Substance Use Disorders with Pregnancy Timing and Intention,” Journal of Women’s Health, November 9, 2022.

“Interconnections between unintended pregnancy, alcohol and other drug use, and pregnancy, birth, infant, childhood and socioeconomic outcomes: a scoping review,” BMJ Sexual & Reproductive Health, October 15, 2024.

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