Adandozan was a king of the Kingdom of Dahomey, in present-day Benin, from 1797 until 1818. His rule ended with a coup by his brother Ghezo who then erased Adandozan from the official history resulting in high uncertainty about many aspects of his life. Adandozan took over from his father Agonglo in 1797 but was quite young at the time and so there was a regent in charge of the kingdom until 1804. Dealing with the economic depression that had defined the administrations of his father Agonglo and grandfather Kpengla, Adandozan tried to reduce slavery to decrease European trade, and when these failed reform the economy to focus on agriculture. Unfortunately, these efforts did not end domestic dissent and in 1818 at the Annual Customs of Dahomey, Ghezo and Francisco Félix de Sousa, a powerful Brazilian slave trader, organized a coup d'état and replaced Adandozan. He was left alive and lived until the 1860s hidden in the palaces while he was largely erased from official royal history.

Agonglo's (1789-1797) reign had been very contentious ending in his assassination by a brother, Dogan. The slave trade had been largely disrupted for two decades by the Oyo empire, the lack of military success by Dahomey, and European traders changing their focus (the French abolished slavery in 1794 and the British and Portuguese had stopped relying on Dahomey's ports). The result was that when Agonglo died there was a large scale upheaval led by various factions, but this ended on May 5, 1797 with the appointment of Adandozan, the second oldest son of Agonglo as the new king. However, because Adandozan was young at the time, the first seven years of his rule were held by a regency of various elder statesmen. In 1804, he became old enough to formally rule with his own authority but the regency members retained importance.

One story contends that Adandozan's younger brother Ghezo had actually been named the heir to Agonglo and that Adandozan was merely a regent. However, that Adondozan refused to relinquish the throne when Ghezo was old enough. This story is doubted by historian Akinjogbin as an invention by Ghezo to justify his coup against Adandozan.

Adandozan followed Agonglo's policies of trying to revive the slave trade through slave raiding of the Mahi people to the north and disrupting the trade at rival ports (namely Porto-Novo). However, these attempts were generally unsuccessful and with the recovery of the Oyo empire by 1805, they reasserted power and stopped these activities by Adandozan.

Unable to foster the slave trade through military action, he turned to improving diplomacy with European traders. In 1804, he sent ambassadors to Portugal and to the British at Cape Coast Castle. Unlike his father who had received Catholic missionaries from the Portuguese, Adandozan made clear that he had no interest in conversion but requested the Portuguese help him in building mining operations and a gun manufacturing facility in Dahomey. The Portuguese received these requests politely to secure the release of some Portuguese prisoners, but did not agree to the terms. The British had grown highly suspicious of Adandozan when the British officer in the port city of Whydah, who had become a citizen of Dahomey, had died in 1803 and, as per the customs, his wives were taken by the king. His assistant wrote to the British calling Adandozan a tyrant and this increased tension with the British. Adandozan, worried that the British would abandon their fort in Whydah, passed a law that any British person in Dahomey could not leave without a substitute which only ended increasing tensions.

Adandozan responded to the slowing of the slave trade by trying to reform the economy to focus on agricultural production. He increased opportunities for agriculture and made the Corn Customs a primary festival held publicly. While attempting these reforms, changed policies in Europe largely undermined his efforts. The British abolished the slave trade in 1807 and began pressuring other countries in Europe to do the same. As part of these efforts they signed an agreement in 1810 with the Portuguese which allowed slave trade only at ports where the Portuguese already traded slaves and no new ports, Whydah was specifically mentioned as a port which could have trade while Porto-Novo, Badagry, and Little Popo (all rival slave trade ports) could not. The result was a sudden increase in the Portuguese slave trade in Whydah.

The increased slave trade simultaneously undermined the agricultural reforms of Adandozan and increased the power of Francisco Félix de Sousa, a powerful Brazilian slave trader. By 1810, de Sousa had become the wealthiest trader in the city of Whydah and loaned significant amounts of money to Adandozan. When he requested repayment for this loan, Adandozan publicly insulted de Sousa and imprisoned him causing de Sousa to flee to Little Popo. One of Adandozan's younger brothers, Ghezo (then called Madogungun), befriended de Sousa and together the plotted a coup to replace Adandozan.

There is little evidence about the last years of Adandozan's reign and the specifics of the coup to replace him are detailed very differently in different sources; even the year of the coup is not agreed upon.