From the time of Ptolemy IV onward, the dynasty's declining prestige abroad was matched by faltering administration at home, though it is hard to decide whether constant dynastic intrigues, minority regencies, military reversals and economic crises were primarily responsible for the breakdown of the system, or whether simmering anarchy and anti-governmental feelings contributed more. At any rate, the royal revenues began to decline as did the Ptolemy's fortunes in general.

Ptolemy IV took the throne in about 222 BC, using the Egyptian name Iwaennetjerwy-menkhwy Setepptah Userkare Sekhemankhamun, a name that means "Heir of the [two] Beneficent Gods, Chosen of Ptah, Powerful is the Soul of Re, Living Image of Amun". 

Unlike his predecessors, this Ptolemy led a dissolute life, aided and abetted by Sosibius, an Alexandrian Greek who had ingratiated himself into high office and made sure that he was indispensable to the king. Though some recent attempts have been made to credit Ptolemy IV with an active foreign policy, history mostly regards him as one dominated to a great extent by his advisers and women. In fact, probably acting on wild rumors that Sosibius may very well have started, Ptolemy agreed to have his mother, the famous Beerenie II, and his brother Magus respectively poisoned and scalded to death within a year of his accession. 

Then trouble seems to have begun when Antiochus III of Syria, no doubt having heard through his intelligence sources of Egypt's weaknesses under the dissolute king, began to move through Phoenicia taking Egyptian vassal cities during the fourth Syrian War. He captured the port of Seleucia-in-Pieria which had been taken by Ptolemy IV's father, and then Tyre and Ptolemais-Ake surrendered to him, thus leaving the road through Palestine to Egypt open to him. Had Antiochus III been a better military man, he would have probably marched on against the Egyptian fortress of Pelusium, which could not have withstood him. However, Potlemy IV's diplomats stalled him with peace talks producing a four month truce which Ptolemy IV, with Sosibius' aid, used to recruit foreign mercenaries as well as raise and train an Egyptian army of some thirty thousand men. 

In the summer of 217 BC, at the head of a fifty-five thousand man army and accompanied by his young sister, Arsinoe, Ptolemy IV took the field in person to face Antiochus III's army of sixty-eight thousand at Raphia in Palestine, just beyond the Egyptian frontier. Here, Ptolemy IV defeated Antiochus III, and relieved Egypt of the threat of invasion.  Interestingly, Ptolemy employed forest elephants, a small variety from Somalia against Antiochus III's larger African bush (some say Indian) elephants. Those of Ptolemy were scared off by the larger elephants, and at first the battle went against the Egyptians, but Antiochus III overextended himself, leaving himself open for the defeat in a pitched battle considered one of the largest of this period. However, this victory bought little gain to Egypt, and in the end, would prove troublesome because of the now well trained Egyptian troops.

Ptolemy IV spent another thee months settling affairs in the Egyptian controlled region before heading home. This was really a short period of time, and better men might have stayed to take advantage of the situation, but some believe the king was apparently eager to return to the luxuries of Alexandria. For example, he left the important port of Seleucia-in-Pieria, which his father had taken in the first place, in the hands of Antiochus III. However, his reluctance to purse these military matters may have been somewhat more complex. A fall in population and a shrinkage of overseas trade had brought about an acute shortage of silver in Egypt and only seven years after Raphia, silver seems to have been abandoned altogether as Ptolemaic Egypt's standard currency. It might have been understandable that Ptolemy IV balked at hiring the extra mercenaries needed to pursue an aggressive foreign policy, and the financial considerations may have even dictated his later disastrous enrollment of Egyptian troops. 

After returning to Egypt, he married his sister in October of 217 BC and the two received a cult as the "Father-Loving Gods" (Theoi Philpatores). She provided an heir seven years later, but afterwards, Ptolemy IV tuned his affections to another woman named Agathoclea, who he took as a mistress. With her brother Agathocles, they encouraged his excesses. Now, though the true deterioration only may have set in about the time of Ptolemy IV's death in about 204 BC, or shortly before, events in Egypt took on a vicious cycle. 

The Egyptian troops trained under the king stimulated a strong nationalist movement which resulted, at first, in a long and successful guerilla campaign against the Alexandria court. Indeed, by the end of his reign, they were able to achieve total independence in the south, which for a time was ruled once more by native pharaohs. During the period of rebel insurrection, an increased army of mercenaries was needed to fend off their constant marauding, further draining capital and resulting in a cutback in overseas trade, which in turn made the economic situation even worse. 

Nevertheless, scholarship in Alexandria went on unabated. Ptolemy IV himself was a dabbler in the arts and in this regard a free thinker who wrote a tragedy entitled Adonis, and presumably played the lead. He actually founded a Homereion, a shrine honoring Homer, with inside it a statue of the poet surrounded by personified figures of the cities that claimed to be his birthplace. At the same time, one must wonder about the works that were composed during this period. One story tells of a poetry competition during his reign. In it, all of the judges ranked the poetry according to the amount of applause it received, with the exception of Aristophanes of Byzantium. He chose the one who received the least applause. When asked for an explanation, he retreated to the great Library, retrieving texts that showed his candidate was the only original poet. All the others had simply been plagiarizing their predecessors.

One of Ptolemy IV's other accomplishments, more of a tidbit of trivia than anything else, was the building a a huge, though apparently non-functioning and immovable ship measuring some 420 feet in length with a capacity to hold some 2,850 marines.

He also did some work at the Temple of Isis at Philae, at Tanis, at the Temple of Montu at Medamud, at the Ptolemaic Temple of Hathor on the West Bank at Thebes (modern Luxor), at the Khonsu Temple at Karnak, and probably at the Temple of Horus at Edfu. 

After Ptolemy IV's death in the summer of 204, he was doubtless buried in Alexandria, but more intrigue was to follow. Arsinoe III had, in fact, remained his wife, at least in name, and her son Ptolemy V was still a child. She was eager to rule through her son, but so to was Sosibius and Agathocles, who had also become a powerful minister. They had Arsinoe III murdered, and while we do not know of Sosibius' fate, Agathocles briefly became regent using a forged will of Ptolemy IV. However, this did not set well with the Alexandrians and he was soon lynched by the Alexandrian mob, which was now emerging as an active, if not organized political force. They then went after his relatives and associates, and Polybius tells us that:

"All of them were then handed over together to the mod, and some began to bite them, others to stab them, others to gouge out their eyes. As soon as any of them fell, the body was torn limb from limb until they had mutilated them all"

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