BACKGROUND: Antiplatelet agents may be useful for the treatment of deep venous thrombosis (DVT) when used in addition to best medical practice (BMP), which includes anticoagulation, compression stockings, and clinical care such as physical exercise, skin hydration, etc. Antiplatelet agents could minimise complications such as post-thrombotic syndrome (PTS) and pulmonary embolism (PE). They may also reduce the recurrence of the disease (recurrent venous thromboembolism (recurrent VTE)). However, antiplatelet agents may increase the likelihood of bleeding events. OBJECTIVES: To assess the effects of antiplatelet agents in addition to current BMP compared to current BMP (with or without placebo) for the treatment of DVT. SEARCH METHODS: The Cochrane Vascular Information Specialist searched the Cochrane Vascular Specialised Register, CENTRAL, MEDLINE, Embase and CINAHL databases and World Health Organization International Clinical Trials Registry Platform and ClinicalTrials.gov trials registers to 7 December 2021. The review authors searched LILACS and IBECS databases (15 December 2021) and also checked the bibliographies of included trials for further references to relevant trials, and contacted specialists in the field, manufacturers and authors of the included trials. SELECTION CRITERIA: We considered randomised controlled trials (RCTs) examining antiplatelet agents compared to BMP following initial standard anticoagulation treatment for DVT. We included studies where antiplatelet agents were given in addition to current BMP compared to current BMP (with or without placebo) for the treatment of DVT (acute: treatment started within 21 days of symptom onset; chronic: treatment started after 21 days of symptom onset). We evaluated only RCTs where the antiplatelet agents were the unique difference between the groups (intervention and control). DATA COLLECTION AND ANALYSIS: We used standard Cochrane methodological procedures. Two review authors independently extracted data and assessed risk of bias of the trials. Any disagreements were resolved by discussion with a third review author. We calculated outcome effects using risk ratio (RR) or mean difference (MD) with a 95% confidence interval (CI) and the number needed to treat to benefit (NNTB). MAIN RESULTS: We included six studies with 1625 eligible participants, with data up to 37.2 months of follow-up. For one preplanned comparison (i.e. antiplatelet agents plus BMP versus BMP plus placebo) for acute DVT we identified no eligible studies for inclusion. In acute DVT, antiplatelet agents plus BMP versus BMP alone was assessed by one study (500 participants), which reported on four outcomes until 6 months of follow-up. There were no deaths and no cases of major bleeding reported. The participants who received antiplatelet agents showed a lower risk of PTS (RR 0.74, 95% CI 0.61 to 0.91; 1 study, 500 participants; very low-certainty evidence). The control group presented a lower risk of adverse events compared to the intervention group (RR 2.88, 95% CI 1.06 to 7.80; 1 study, 500 participants; very low-certainty evidence). This study did not provide information for recurrent VTE or PE. In chronic DVT, antiplatelet agents plus BMP versus BMP alone was assessed by one study (224 participants). The study authors reported four relevant outcomes, three of which (major bleeding, mortality and adverse events) showed no events during the 3 years of follow-up. Therefore, an effect estimate could only be reported for recurrent VTE, favouring antiplatelet agents plus BMP versus BMP alone (RR 0.12, 95% CI 0.05 to 0.34; 1 study, 224 participants; very low-certainty evidence). For the outcomes PE and PTS, this study did not present information which could be used for analysis. In chronic DVT, antiplatelet agents plus BMP versus BMP plus placebo was assessed by four studies (901 participants). The meta-analysis of this pooled data showed a lower risk of recurrent VTE for the antiplatelet agents group (RR 0.65, 95%, CI 0.43 to 0.96; NNTB = 14; low-certainty evidence). For major bleeding, we found no clear difference between placebo and intervention groups until 37.2 months of follow-up (RR 0.98, 95% CI 0.29 to 3.34; 1 study, 583 participants; moderate-certainty evidence). In PE fatal/non-fatal outcome, we found no clear difference with the use of antiplatelet agents (RR 0.52, 95% CI 0.23 to 1.14; 1 study, 583 participants; moderate-certainty evidence). For all-cause mortality, the overall effect of antiplatelet agents did not differ from the placebo group (RR 0.48, 95% CI 0.21 to 1.06; 3 studies, 649 participants; moderate-certainty evidence). The adverse events outcome did not show a clear difference (RR 1.57, 95% CI 0.34 to 7.19; 2 studies, 621 participants; moderate-certainty evidence). There is no assessment of PTS in these studies. We downgraded the certainty of evidence for risk of bias, indirectness, imprecision and publication bias. AUTHORS' CONCLUSIONS: In chronic DVT settings, following the initial standard treatment with anticoagulants, there is low-certainty evidence that antiplatelet agents in addition to BMP may reduce recurrent VTE, (NNTB = 14) when compared to BMP plus placebo. Moderate-certainty evidence shows no clear difference in adverse events, major bleeding and PE when antiplatelet agents are used in addition to BMP compared to BMP plus placebo. In acute and chronic DVT settings, following the initial standard treatment with anticoagulants, we can draw no conclusions for antiplatelet agents in addition to BMP compared to BMP alone due to very low-certainty evidence.  Trials of high methodological quality, that are large and of sufficient duration to detect significant clinical outcomes are needed. Trials should ideally last more than 4 years in order to estimate the long-term effect of antiplatelet agents. Trials should include people with acute and chronic DVT and provide relevant individual data, such as the outcome for each index event (DVT or PE), the use of an inferior vena cava (IVC) filter, whether the DVT is provoked or unprovoked, and the age of participants.